Conventionally, bearings made of sintered parts with various compositions are used for internal combustion engines of automobiles.
Particularly, in the oil-impregnated sintered bearing in which lubrication is obtained by retaining lubrication oil in pores, it is known that the Cu-based material is useful to obtain low friction coefficient. Particularly, seizure can be suppressed by using the bearing made of the Cu-based sintered part (Cu-based sintered bearing) for supporting the rotating shaft made of the Fe-based alloy.
On the other hand, as the bearing for the use in which high surface pressure is placed by loading, vibration or the like, the iron-based or the iron-copper-based sintered part has been used in order to sustain the high surface pressure. However, the iron-based or the iron-copper-based sintered part has high friction coefficient, and is not suitable for use in which high precision control is required, such as being used for the bush of the throttle valve and the like. Thus, the ball bearing is used instead, which causes cost increase.
Recently, for the sake of cost reduction and the like, using the Cu-based sintered part as these bearings that requires the high precision control is demanded.
As the Cu-based sintered part, there are ones made of: the bronze-based material; the phosphor-bronze-based material; and the copper-nickel-based material. Among these, the bronze-based material and the phosphor-bronze-based material have low material strength to begin with and cannot be used in the condition where the high surface pressure is placed. On the other hand, strength is increased by adding a large amount of Ni in the Cu-based sintered part made of the copper-nickel-based material. The sintered part made of the copper-nickel-based material is regarded as a promising sintered part applicable for the part to be exposed to the high surface pressure and to be controlled with high precision.
As the Cu-based sintered part made of the Cu—Ni-based material, there are ones disclosed in Patent Literature 1 (PTL 1) and Patent Literature 2 (PTL 2).